A device of this type is known (German OS 3 610 363). These known devices have on the whole proven practical.
They do have the drawback, however, of complexity. When the devices are manufactured in the form of probes, they must be gas tight and subjected subsequent to manufacture to a gas-tightness testing, increasing the prime cost of the probe. The probe cylinder must also accommodate a separate heater, which makes it larger and deteriorating the transfer of heat between the heater and the cylinder, entailing such additional drawbacks as high energy consumption and a non-uniform distribution of temperatures. Such a device occupies considerable space. Furthermore, the large masses take time to heat up, and the device cannot be operated until at least 60 seconds after it has been turned on. Again, relatively a lot of power is consumed in heating through the operation. Another essential drawback to the known system aside from its inertia is its only moderate precision, which results from the temperature sensitivity of the signals deriving from the sensor. Finally, a reference-gas mixture in the form of air must be supplied to the known device, meaning not only that the housing must be more complicated but that it cannot be installed anywhere desired.
Compensating for the temperature dependence of the known devices by incorporating a temperature sensor and computerized controls has already been conceived of. Such a device, however, is not yet known.